Caries is the decay of tooth or bone. Dental caries (also known as dental decay, caries or carious lesions) is caused by acids produced by microbial enzymatic action on ingested carbohydrate. The acids decalcify (demineralise) the inorganic portion of the tooth initially creating a sub-surface lesion, the organic portion then disintegrates leading to the creation of a cavity. In dentistry, demineralisation of a tooth through the development of a carious lesion can be described in terms of the depth of the carious lesion.
Dental caries is commonly treated by the removal of the decayed material in the tooth and the filling of the resultant hole (cavity) with a dental amalgam or other restorative material. In more severe cases, the entire tooth may be removed. Prior to lesion cavitation, it is possible to heal or reverse the tissue destruction by remineralising the caries lesions. However, this process works better where exogenous (e.g. salivary- or food-derived) proteins and lipids have been removed from the caries lesions.
It is known that the level of tooth decay alters the electrical characteristics of a tooth. This arises because as minerals are lost the porosity of the tooth increases and the consequent increased numbers of ions within the pores increase the conductivity i.e. the electrical transport in the tooth. Consequently, demineralisation of a tooth will result in an enhancement of its charge transport properties. This may be manifested in a decrease in the potential difference which must be applied to a demineralised tooth, compared with a healthy tooth, in order to achieve a comparable current therethrough. Correspondingly, this may be manifested in an increased current measurable from a demineralised tooth, compared with a healthy tooth, on application of the same potential difference. These effects can be detected on application of a constant current or constant potential difference respectively. Alternatively, the impedance (which includes the DC resistance) can be monitored by using AC signals.
There are a number of devices specifically designed to detect dental caries by the application of an alternating electrical current to a tooth using a probe or contact electrode and counter electrode. As described above, the main source of impedance in the circuit formed by the counter electrode and the probe is provided by the tooth and therefore, changes to the impedance of the circuit give a measure of changes in the impedance of the tooth. This technique is described in international patent application WO97/42909.
Iontophoresis is a non-invasive method of propelling a charged substance, normally a medication or a bioactive agent, using an electric current. It is known to use iontophoresis in transdermal drug delivery. Iontophoresis may also be used in conjunction with fluoride containing compounds to treat dentine hypersensitivity and to remineralise non-cavitated dental caries lesions. Iontophoresis devices typically include an active electrode assembly and a counter electrode assembly each coupled to opposite poles or terminals of a voltage source. The active agent can be cationic or anionic and the voltage source can be configured to apply the appropriate voltage polarity based upon the polarity of the active agent. The active agent may be stored in for example, a reservoir such as a cavity or in a porous structure or a gel.